丢失片段更改的数据答案

【问题标题】：Losing data on fragment change丢失片段更改的数据
【发布时间】：2018-04-25 11:16:14
【问题描述】：

你能帮我解决这个问题吗？

我有一个底部导航栏的活动，它改变了中间的片段。其中一个选项是使用选项卡显示分为 2 组的项目列表。在我第一次打开片段时，所有数据都按预期存在，但是我更改片段并再次使用列表调用片段的 newInstance，所有数据都消失了。请查看下面的 GIF 以更好地理解：

下面是设置标签的代码：

 private void setViewPager(){
        List<Fragment> frag = new ArrayList<>();
        frag.add(MyReservationsFragment.newInstance(true));
        frag.add(MyReservationsFragment.newInstance(false));

        MyViewPagerAdapter myViewPagerAdapter = new MyViewPagerAdapter(getFragmentManager(), frag, getContext());
        vpaReservations.setAdapter(myViewPagerAdapter);
        tabReservations.addTab(tabReservations.newTab().setText(getString(R.string.s_tab_1)));
        tabReservations.addTab(tabReservations.newTab().setText(getString(R.string.s_tab_2)));
        tabReservations.setupWithViewPager(vpaReservations);
    }

下面是我如何实例化每个片段：

public class MyReservationsFragment extends Fragment implements MyReservationsContract.View{

    private static final String TAG = "MyResFrag";
    private static final String ONLY_PENDING = "onlyPending";
    private static final String RESERVATION_ID = "reservationId";

    @BindView(R.id.rvi_my_reservations) protected RecyclerView rviMyReservations;

    private boolean onlyPending;
    private MyReservationsContract.Presenter mPresenter;


    public MyReservationsFragment() {
        // Required empty public constructor
    }

    public static MyReservationsFragment newInstance(boolean onlyPending) {
        MyReservationsFragment frag = new MyReservationsFragment();
        Bundle args = new Bundle();
        args.putBoolean(ONLY_PENDING, onlyPending);
        frag.setArguments(args);

        return frag;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            onlyPending = getArguments().getBoolean(ONLY_PENDING);
        }

        mPresenter=new MyReservationsPresenter();

    }

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.frag_reservations_list, container, false);
        ButterKnife.bind(this, view);
        return view;
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
//        List<MyReservation> myReservations = Const.getMyReservations(onlyPending);

        List<Reservation> myReservations = mPresenter.getUserReservationsByStatus(onlyPending);
        setRecyclerView(myReservations);
    }

    private void setRecyclerView(final List<Reservation> myReservations){
        rviMyReservations.setHasFixedSize(true);
        LinearLayoutManager mLayoutManager = new LinearLayoutManager(getActivity());
        rviMyReservations.setLayoutManager(mLayoutManager);

        MyReservationAdapter mAdapter = new MyReservationAdapter(myReservations,getContext());
        mAdapter.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int position = rviMyReservations.getChildLayoutPosition(view);
                Intent intent = new Intent(getActivity(), ReservationDetailActivity.class);
                intent.putExtra(RESERVATION_ID, myReservations.get(position).getId());
                startActivity(intent);
            }
        });

        rviMyReservations.setAdapter(mAdapter);
        rviMyReservations.setItemAnimator(new DefaultItemAnimator());
    }


}

我已经尝试保存“onlyPending”变量的标志，但由于片段没有被破坏，它具有相同的行为。我已经卡了2天了，你们能帮帮我吗？

【问题讨论】：

标签： android fragment tabview

【解决方案1】：

不要每次都使用 new 运算符创建实例，片段的新对象将被创建，旧数据将消失。所以像这样创建，

片段类中的第一个：

  public static  MyReservationsFragment frag;

在newInstance方法中：

public static MyReservationsFragment newInstance(boolean onlyPending) {
    if(frag == null)
    {
         frag = new MyReservationsFragment();
    }

    Bundle args = new Bundle();
    args.putBoolean(ONLY_PENDING, onlyPending);
    frag.setArguments(args);

    return frag;
}

【讨论】：